The present invention relates to the preparation of methacrylimide (also known as glutarimide) containing polymers additionally containing C.sub.2-20 alkyl or cycloalkyl methacrylate ester functionality. More particularly the present invention relates to such a process for the selective conversion of methyl methacrylate functionality to methacrylimide functionality in a starting resin comprising methyl methacrylate and C.sub.2-20 alkyl or cycloalkyl methacrylate functionality via an amidization and imidization process. In a preferred embodiment the polymers prepared according to the present process additionally comprise functionality derived from monovinylidene aromatic monomers. Polymers prepared according to the present process desirably have extremely low birefringence, high heat resistance and low moisture absorption making them especially well suited in the preparation of optical storage media such as digital audio disks and computer memory devices.
In Ser. No. 173,688, filed Mar. 25, 1988, now abandoned, there are disclosed intrinsically low birefringent molding polymers comprising methacrylimide functionality and alkyl methacrylates having greater than 1 carbon in the alkyl group. The use of such hindered or bulky methacrylates were found to be necessary to substantially reduce moisture uptake of the resulting polymers.
It is previously known in the art to convert methyl methacrylate containing polymers via an amidization and imidization process to the corresponding methacrylimide containing polymers. In U.S. Pat. Nos. 4,246,374 and 4,745,159 processes employing extruders and binary solvent combinations for such polymer preparation are disclosed.
For the teachings contained therein all of the foregoing patents and the pending United States patent application are incorporated herein by reference thereto.
It would be desirable if there were provided a convenient process utilizing the extruder or solution amidization and imidization techniques disclosed in the foregoing references to prepare polymers containing C.sub.2-20 alkyl or cycloalkyl methacrylate ester functionality.